Electrical connecting means and contact elements of such means



Sept. 25. 1956 H. J. MODREY ELECTRICAL CONNECTING MEANS AND CONTACT ELEMENTS OF SUCH MEANS 2 Sheets-Sheet 1 Filed April 3, 1953 Mmver/c FE/U INVENTOR.

HENRY J. MODREY N! 3 HQ ATTORNEY Sept. 25, 1956 H. J. MODREY 2,764,747

ELECTRICAL CONNECTING MEANS AND CONTACT ELEMENTS OF SUCH MEANS 2 Sheets-Sheet 2 Filed April s, 1955 M/q GNET/C Eric MAGNET/C 56 55 MAGNET/C MAGNET/C INVENTOR.

HENRY J. MODREY BY ATTORNEY United States Patent ELECTRICAL CONNETING MEANS AND CON- T ACT ELEMENTS 0F SUCH MEANS Henry J. Modrey, Stamford, Conn.

Application April 3, 1953, Serial No. 346,690

29 Claims. (Cl. 339-12) The present invention relates to electrical connecting means and contact elements, particularly to electrical connecting means in which one contact element is insertable in another contact element.

Among the now preferred fields of application of the invention are single and multi-pole connectors both of the round pin and the flat blade type; contact elements of electron tube bases; and generally engaging and receiving contact elements in coacting electrical components.

Contact between the engaging and receiving elements of connecting means of the general type above referred to, is effected by a frictional pressure engagement.

Whatever the specific design and arrangement of the contact elements to be engaged may be, the basic problem is always the same, namely, to maintain a low constant resistance value between the engaged contact elements. The importance of this problem is particularly great in the electronic field which generally requires high quality connections.

Contactquality depends primarily upon the degree and constancy of the frictional pressure between the coacting surfaces of the contact elements. It is subject to two factors, namely, burnishing and contact fatigue. Burnishing is caused by the relative sliding of the contact elements during repeated insertions and withdrawals of the contact elements. Microscopic examination shows that the entire or substantially entire surface of say a contact pin is never in metallic engagement with substantially the entire surface of the socket in which the pin is inserted, but the contact is in fact made by a multitude of minute high spots on the contact surfaces. These high spots are gradually smoothed or burnished which results in a deterioration of the contact quality.

Contact fatigue is due to a gradual decrease in the pressure by which the contact elements are pressed together. The springiness of the contact material itself or that of auxiliary external springs gradually diminishes due to aging and repeated deformations caused by insertion and withdrawal of the pin or other contact element. In practice, the initial spring pressure of rolled or slotted contact material decreases rather rapidly as the contacts are generally very small.

There is not known at the present time a reliable method of determining directly the frictional contact pressure between engaged pin and blade type contacts. It is customary to employ a substitute measurement for the determination of actual contact pressure, namely, the withdrawal pull of the plug from the socket. Tests carried out on this basis with various standard designs of contact elements of connectors show that the withdrawal pull decreases after a limited number of insertions below an acceptable value and that the contact resistance increases above an acceptable value.

One of the principal objects of the invention is to provide novel and improved coacting contact elements that are held in conductive engagement by a force which is constant and permanent for all practical purposes.

Another object of the invention is to provide novel and improved coacting contact means whose withdrawal pull remains high and whose contact resistance remains within acceptable limits after a very great number of insertions and withdrawals.

Still another object of the invention is to provide coacting contact elements which remain in intimate conductive engagement even though an initially effective spring action has practically disappeared due to fatigue of the springy component, and friction between the contact elements has become very low due to burnishing caused by frequent insertions and withdrawals.

A further object of the invention is to provide means of permitting the manufacture of coacting elements of small size which have a constant and permanently low contact resistance. As previously mentioned, the manufacture of small sized coacting contact elements relying on friction for low contact resistance is particularly difficult as the springy components forming the engaging surfaces must be correspondingly small.

A still further object of the invention is to provide means by which the aforementioned advantages are attained without an appreciable increase in the size of the contact elements.

Generally speaking, the invention resides in providing contact elements the electrically conducting material of which is combined with magnetic material so disposed that the contact pressure between the conducting portions of the contact elements is increased by magnetic attraction. As a result, the initial low contact resistance remains constant for all practical purposes. Furthermore, a non-intentional separation of the contact elements is eifectively prevented whereas standard contact elements tend to fall apart or become separated by the slightest pull when the initially efiective spring action pressing the contact elements together, has more or less disappeared due to fatigue.

Other and further objects, features and advantages of the invention will be pointed out hereinafter and set forth in the appended claims forming part of the application.

In the accompanying drawing several now preferred embodiments of the invention are shown by way of illustration and not by way of limitation.

In the drawing:

Fig. 1 is a side view, .partly in section, of a round contact pin according to the invention.

Fig. 2 is a side view of a modification of a round contact pin, also partly in section.

Fig. 3 is a side view of another modification of a round contact pin.

Fig. 4 is a section taken on line 4-4 of Fig. 1.

Fig. 5 is a section taken on line 55 of Fig. 3.

Fig. 6 is an isometric view of the magnetic component of the pin according to Fig. 3.

Fig. 7 is a side view, partly in section, of a socket for receiving a round contact pin.

Fig. 8 is a section taken on line 88 of Fig. 7.

Fig. 9 is a side view of a modification of a socket for a round contact pin.

Fig. 10 is a section taken on line 10-10 of Fig. 9.

Fig. 11 is a sectional view of a modification of the socket of Fig. 9.

Fig. 12 is a sectional view of another modification of the socket of Fig. 9.

Fig. 13 is an isometric view of a multi-pole connector employing round contact pins according to the invention.

Fig. 14 is a perspective view of a fiat contact pin according to the invention.

Fig. 15 is a section along line 15-15 of Fig. 14.

Fig. 16 is a perspective view of a modification of Fig. 14.

Fig. 17 is a section taken on line 1717 of Fig. 15.

a.) Fig. 18 is a sectional view of a modification of the contact pin of Fig. 16.

Fig. 19 is a perspective view of a socket according to the invention for receiving a flat contact pin.

Fig. 20 is a modification of the socket according to' Fig. 19, and

Fig. 21 is a perspective view of a modification of the socket according to Figs. 19 and 20. v

Referring first to Fig. 1 and its cross-section according to Fig. 4, these figures show an engaging contact element in form of a round pin. In this connection, it should be mentioned that the invention is concerned only with the contact elements themselves. Accordingly, all the figures, with the exception of Fig. 12 whichshows a multi-pole connector by way of example, illustrate the contact ele ments only. The contact elements should be visualized as being simply attached to a wire or mounted on or in a shell or housing or any other support suitable for the purpose.

The contact pin according to Figs. 1 and 4, comprises an outer sleeve 20 made of any electrically conductive material suitable and known for the purpose and an inner sleeve 21 made of magnetic or magnetizable material.

The two sleeves are formed with an axial slot 22.

Figs. 7 and 8 show a socket suitable to receive the contact pin according to Figs. 1 and 4. The socket is comprised of an inner electrically conductive sleeve 23 and an outer sleeve 24 made of magnetic or magnetizable material. Both sleeves 23 and 24 are shown as being formed with an axial slot 25. Of course, at least one of the sleeves 21 and 24 must be magnetized.

While both the socket and the contact pin are shown slotted, it is sufiicient when only one of these elements, generally the socket, is slotted to provide the necessary spring tension.

As will be apparent, sleeves 21 and 24 will attract each other when the contact pin of Fig. l is inserted in the socket of Fig. 7, slots 22 and 25 permitting a slight contraction of the diameters of the sleeves thereby pulling the mating contact surfaces into a more intimate engagement. As a result, the contact pressure between the engaging surfaces of sleeves 20 and 23 is correspondingly increased. As is well known, magnetic attraction does not appreciably age, but remains permanently constant for all practical purposes. Accordingly, contact pressure is retained even though an initially effective springiness inherent in the coacting contact elements may have practically disappeared due to fatigue.

Extensive tests have shown that the contact pressure obtained by magnetic attraction only can be made sufficient to result in an acceptable contact resistance and also to prevent a falling apart of the contact elements.

The two sleeves of both the contact pin and the socket may be formed from thin sheet metal. As obviously the magnetic attraction is the higher the thinner the separating layers of conductive material, generally a non-magnetic material, are, it is advantageous to make the conductive sleeves as thin as possible. Applicant has found that good results are obtained when magnetic sheet steel is rolled and made integral with a thin layer of contact material such as copper or silver.

Advantageous results are also obtained by plating respective sides of a contact pin or socket sleeve made of magnetic material with copper or other well conducting material; for instance, shells 21 and 23 may be made of magnetized steel sheets and plated first with nickel for resistance to corrosion, then with copper and finally with silver. Plating produces the thinnest possible layer between the coacting magnetic components of the contact elements and is suflicient for small currents as are generally used in electronic equipment.

Fig. 2 shows a contact pin which is particularly suitable for contact elements of a very small size and is capable of a strong magnetic action in relation to its size. According to Fig. 2 a magnetic core 26 in form of magnetized electrically conductive material such as copper.

wire is inserted in a shell 27 of suitable conductive material.

The contact pin according to Fig. 2 may be inserted in the socket according to Fig. 7 in which case the contact pressure between the contact sleeves 24 and 27 will be increased by the magnetic attraction between shell 23 and core 26. It is, of course, also possible to provide a soft iron wire 26 and a magnetized shell 23.

Figs. 9 and 10 show a socket which is suitable for coaction with the pins according to Figs. 1 and 2 and primarily designed for larger sizes of contact elements.

The socket according to Figs. 9 and 10 comprises a shell 28 made of electrically conductive material such as copper. The shell is formed with an axial slot 29. The edges of the shell defining this slot are turned or rolled over to form two sleeves 30 and 31 in which are tightly fitted magnetic wires 32 and 337 As appears from the previous description, wires 32 and 33 will attract the magnetic component of a contact pin inserted in the circuit member thereby increasing the contact pressure. In addition, wires 32 and 33 attract each other. By making the material of shell 28 sufficiently thin and flexible the magnetic wires will tend to tighten the sleeve over the plug contact, not unlike a hose clamp. Asa result of the lateral attraction of wires 32 and 33 a certain increase in the contact pressure will also be attained when a standard contact pin, that is, a contact pin which is not combined with a magnetic component, is inserted in the socket according to Fig. 9.

The socket pin according to Fig. 11 uses the same principle as the socket according to Figs. 9 and 10. The socket of Fig. 11 comprises a slotted sleeve 34 made of The ends of the sleeve are turned inwardly to retain two magnetic wires 32 and 33. As a result, the magnetic wires are separated from the magnetic material of the plug pin by only one layer of non-magnetic material, thereby increasing the effective magnetic attraction. Furthermore, the air gap between wires 32 and 33 is reduced thereby increasing the lateral magnetic attraction between these two wires which tends to pull together the sleeve over the inserted contact pin. To achieve the best possible result the metal wires are preferably so positioned that they touch the interior periphery of shell 34, thereby reducing to a minimum the gap between the magnetic material of the contact pin and wires 32 and 33.

The socket according to Fig. 11 is also effective in coaction with a non-magnetic contact pin provided the wall of shell 34 is sufficiently thin and flexible to permit circumferential contraction of the shell.

Fig. 12 shows a socket design according to which the effect of the attraction between wires 32 and 33 is further increased by providing a socket shell composed of halves 35 and 36 hinged together by means of a hinge pin 37. This figure also shows that the socket halves are held in intimate contact with an inserted plug pin 38 which may or may not comprise a magnetic component.

Figs. 3, 5 and 6 show a contact pin which is particularly suitable for larger size contact pins or for applications in which plating alone does not produce an efficient conductive surface or in which a rapid abrasion of the plating must be anticipated. According to Figs. 3 and 5, the contact pin comprises a shell 40 made of a suitable electrically conductive material and formed with a rather wide slot 41. A liner 42 made of magnetic or magnetizable springy material is fitted in shell 40. As can best be seen in Fig. 6 the liner is also axially slotted at 44 and provided with a radially protruding longitudinal rib 43. The liner is fitted in shell 40 in a position such that rib 43 is in registry with slot 41 substantially filling the same. As can best be seen in Fig. 5, the outer diameter of rib 43 is the same as the outer diameter of shell 40 so that the outer wall of rib 43 is in peripheral alignment with the outer wall of shell 40. This has the advantage that when the plug pin of Fig. 3 is inserted in any of the sockets according to Figs. 7 to 12 inclusive, the magnetic gap which must be traversed by the magnetic flux is reduced to one layer of electrically conductive material, whereas with plug pins according to Figs. 1 and 2 the magnetic flux must traverse two layers of conductive material,or in other words, the gap is twice as large. In case the plug pin according to Fig. 3- is inserted in a socket according to Fig. 11 or 12 in a position such that rib 43 faces magnetic wires 32 and 33, direct magnetic contact is obtained and, hence, the maximum magnetic attraction, While providing a sufiicient contact area between the coacting electrically conductive surfaces.

Fig. 13 is a multi-pole connector forming a tube base and of basically conventional design. It comprises a plug component and base or socket component 51. The plug component has a plurality of contact pins such as shown in Fig. 2 and the socket component has a corresponding number of receiving sleeves of the type shown in Fig. 7. The wires are connected with the respective socket sleeves by wire entry holes 52. Contact pins in multi-pole connectors of the type shown are generally mounted loosely and are made to float in their retaining socket sleeves or they are mounted on resilient surfaces so that the coasting contact pairs are not affected by irregularities in the alignment of other contact pairs within the same multi-pole connector. As will be apparent, the eifect of the magnetic attraction between the coacting contact elements is the same as has been previously described in connection with individual plug and socket pins.

Figs. 14 and 15 show a fiat contact blade composed of a central magnetic or magnetized layer sandwiched between two outer electrically conductive layers 56 and 57. According to size and the specific requirements the blade may be formed by riveting the layers together, by using magnetic material with two rolled-on conducting surfaces or by employing magnetic material plated with electrically conductive material.

Fig. 19 shows a socket suitable for receiving the contact blade according to Figs. 14 and 15 and similar in structure to this contact blade in that it comprises a central magnetic or magnetizable layer 60 sandwiched between two outer electrically conductive layers 61 and 62. The outer conductive layer 61 may be omitted, in which case a ,wire may be connected directly to the inner conductive layer 62.

When the contact blade of Fig. 14 is inserted in the socket of Fig. 19, assuming that at least one of the magnetic layers is magnetized, the two shanks of the socket will be attracted toward the blade, thereby increasing the contact pressure between the blade and the socket.

The socket according to Fig. 19 will also be effective when a non-magnetic contact blade is inserted in the same due to the magnetic attraction between the two shanks of the socket assuming that the socket is made of sufliciently thin and flexible material.

Figs. 16 and 17 show afiat contact blade comprising an electrically conductive member 65 in which are inserted one or more plugs 66 of magnetic material. The

blade according to Fig. 16 will effectively coact with a socket according to Fig. 19. As will be observed, the magnetic plug 66 is separated from the magnetic material 60 of the socket by the inner layer 62 only thereby reducing the magnetic gap in comparison with the gap that is present when a blade according to Fig. 14 is inserted in the socket. In the latter case, the magnetic flux lines must traverse the outer conductive layers 56 and 57 of the blade and the inner conductive layers 62 of the socket.

Fig. 20 shows a socket similar in principle to the blade of Figs. 16 and 17 in that magnetic plugs 67 are inserted in the shanks of a member 68 made of electrically conductive material.

6 The socket according to Fig. 20 is suitable for maction with the blade according to Fig. 14 and also with a non-magnetic blade by reason of the magnetic attraction between the pair of magnetic plugs 67 provided that in the latter case the shanks of member 68 are sufficiently flexible. The socket of Fig. 20 is not very suitable for coaction with the blades 16 and 17 as then the surfaces in engagement with each other would be primarily the surfaces of the magnetic plugs rather than the electrically conductive surfaces. However, a blade oi the type as shown in Fig. 16 can be made suitable for coaction with the socket of Fig. 20 by slightly recessing either the magnetic plug 66 of the blade or the magnetic plugs 67 of the socket. Fig. 18 shows a section of the blade in which the magnetic plug 66 is slightly recessed relative to the electrically conductive member 65.

Fig. it shows a socket in which the effect of the magnetic attraction between magnetic plugs 67 is increased by providing two socket parts 69 and 70 hinged together by a hinge pin 71. As a result, plugs 67 can pull the socket shanks tightly against the respective surfaces of an inserted contact blade.

T he socket according to Fig. 21 is suitable for coaction with the blades according to Figs. 14 and 18 and also with a non-magnetic blade.

Applicant is aware of the fact that many magnetic materials, as used as part of the various illustrated contact elements, are also electrically conductive, but the term electrically conductive as herein used refers to the conductive material such as copper or sliver of the contact elements that is intended to carry the current. Furthermore, magnetic material that is classified as an insulator such as various metal oxides is obviously also suitable for the purpose of the invention.

No reference has been made in the previous specification to the polarity of the magnetic material, but it will be evident that the polarity must always be such that the desired magnetic attraction is obtained.

While the invention has been described in detail with respect to certain now preferred examples and embodiments of the invention, it will be understood by those skilled in the art after understanding the invention, that various changes and modifications may be made without departing from the spirit and scope of the invention, and it is intended, therefore, to cover all such changes and modifica ions in the appended claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. An electrical connecting means comprising an engaging contact element and a receiving contact element, the engaging contact element being insertable in the receiving contact element, each of said contact elements including an electrically conductive component and a magnetic component, the conductive component of the engaging contact element encompassing at least partly the magnetic component thereof and the magnetic component of the receiving contact element encompassing at least partly the conductive component thereof so that, upon insertion of the two contact elements one in the other, the conductive components of the two contact elements are in contact with each other and the magnetic components are in positions of mutual magnetic attraction for biasing the conductive components toward each other by said magnetic attraction.

2. An electrical connecting means comprising an engaging contact element and a receiving contact element, at least one of said contact elements including electrically conductive material and magnetic material, said latter contact element having two portions spaced apart and yieldably moveable toward each other, each of said portions including part of said magnetic material for biasing the said portions toward each other by magnetic attraction, the other contact element, uponapplication of the two contact elements to each other, extending between said two portions in metallic contact with the conductive material thereof, the magnetic attraction between the magnetic material included in the said portions effecting a pressure contact between the contact elements.

3. An electrical connecting mean having an engaging contact element and a receiving contact element, the said engaging contact element comprising an outer shell made of electrically conductive material and magnetic material disposed within said shell, and the said receiving contact element comprising an inner shell made of electrically conductive material and magnetic material disposed outside said inner shell closely adjacent thereto, the said two contact elements being insertable, one in the other, with the conductive outer shell of the engaging contact element facing the conductive inner shell of the receiving contact element whereby upon insertion of the engaging contact element in the receiving contact element the said two conductive shells are pressed against each other by magnetic attraction between magnetic material of the two contact elements.

4. An electrical connecting means according to claim 3, wherein the magnetic material of the engaging contact element is in form of a liner fitted in the outer shell thereof.

5. An electrical connecting means according to claim 3, wherein the magnetic material of the engaging contact element is in form of a solid core fitted in the outer shell thereof.

6. An electrical connecting means according to claim 3, wherein the said engaging contact element comprises a hollow elongated tubular member having an axial slot and an outer surface of electrically conductive material, and wherein the magnetic material of the said contact element is in form of a liner fitted in said hollow member, the said liner having a radially protruding axial rib disposed in registry with said slot substantially filling the same.

7. An electrical connecting means having an engaging contact element and a receiving contact element, the engaging contact element comprising a core of magnetic material and a layer of electrically conductive material on the outside of said core, and the receiving contact element comprising a hollow core made of magnetic material and a layer of electrically conductive material on the inside of said latter core, the said contact elements being insertable, one in the other, with the conductive layers of said cores in metallic contact with each other whereby upon insertion of the engaging contact element in the receiving contact element, the attraction of the magnetic material associated with the two contact elements presses said two conductive layers against each other by magnetic attraction.

8. An electrical connecting means having an engaging contact element and a receiving contact element, the engaging contact element comprising an elongated hollow member having an outer surface of electrically conductive material and magnetic material disposed within said hollow member, and the receiving contact member comprising a hollow elongated member having an inner surface of electrically conductive material and magnetic material surrounding said inner surface, insertion of the engaging contact element in the receiving contact element efiecting metallic engagement between the conductive surfaces of said elements, one of said contact elements being axially slotted so as to provide for deformation of the slotted element toward the other element by attraction of the magnetic material associated with the two contact elements.

9. An electrical connecting means having an engaging contact element and a receiving contact element, the engaging contact element being in form of a blade having an electrically conductive outer surface and a component of magnetic material disposed within said blade, and the receiving contact element comprising a member formed with two shanks adapted to receive said blade therebetween, the inside walls of said shanks having an electrically conductive surface and magnetic material secured to at least one of said shanks, the magnetic material of the blade and the magnetic material of the receiving contact element being positioned to attract each other upon insertion of the blade between the shanks, thereby biasing the electrically conductive surfaces of the blade and the respective shank toward each other.

10. An electrical connecting means according to claim 9, wherein the said two shanks are moveable toward each other by magnetic attraction.

11. An electrical connecting means according to claim 9, wherein the said engaging contact element is in form of a flat blade made of magnetic material and covered on at least one side with a layer of electrically conductive material.

12. An electrical connecting means according to claim 9, wherein the said engaging contact element comprises a blade made of electrically conductive material and the magnetic material is fitted in a transverse opening of said blade, and wherein the magnetic material on the receiving contact element is fitted in a transverse opening of the respective shank of the U-shaped member.

13. An electrical connecting means according to claitn 12, wherein one of said magnetic materials is recessed relative to the wall in which it is fitted.

14. A receiving contact element for an electrical connecting means including an engaging contact element and a receiving contact element, the said receiving contact element comprising an electrically conductive component defining a space for receiving the engaging element of the connecting means, said component having parts movable towards each other for reducing the said space, and a magnetic component including magnetic material supported by each of said parts in position of mutual magnetic attraction for moving said parts toward each other by said magnetic attraction.

15. A receiving contact element according to claim 14, wherein the said receiving contact element comprises an elongated inner shell made of electrically conductive material and an elongated outer shell made of magnetic material, the said shells being concentrically disposed closely adjacent to each other and axially slotted.

16. A receiving contact element according to claim 14, wherein the said receiving contact element comprises an axially slotted shell made of electrically conductive material, and wherein the said magnetic material is attached to the shell closely adjacent to each of the edges of the shell defining the slot thereof for pulling the edge portions of the shell toward each other by magnetic attraction.

177 A receiving contact element according to claim 16, wherein the said magnetic material is in form of two elongated strips each disposed on the outside of the shell along one of said slot defining edges for pulling the said edge portions toward each other.

18. A receiving contact element according to claim 16, wherein the said magnetic material is in form of two elongated strips each disposed on the inside of the shell along one of said slot defining edges for pulling the said edge portions toward each other.

19. A receiving contact element for an electrical connecting means including an engaging contact element and a receiving contact element, the said receiving con tact element comprising a member having two shanks providing space therebetween for the insertion of an engaging contact element, at least the inner sides of the shanks facing each other being made of electrically conductive material, the said shanks being movable toward each other, and magnetic material forming part of at least one of said shanks.

20. A receiving contact element for an electrical connecting means including an engaging contact element and a receiving contact element, the said receiving contact element comprising a member having two shanks providing space therebetween for the insertion of an engaging contact element, at least the inner sides of the shanks facing each other being made of electrically conductive material, the said shanks being movable toward each other, and magnetic material forming part of both said shanks and disposed in position for mutual magnetic attraction thereby pulling the two shanks toward each other.

21. A receiving contact element according to claim 20, wherein the said shanks are made of magnetic material, the inside of said shanks being covered with a layer of electrically conductive material.

22. A receiving element according to claim 20, wherein the said shanks are made of electrically conductive material, and wherein magnetic material is fixedly secured in a transverse opening in each shank, the magnetic materials in the two shanks facing each other for attracting :the two shanks toward each other.

23. A receiving contact element according to claim 22, wherein the said magnetic materials are recessed relative to the inner wall of the respective shank.

24. A receiving contact element according to claim '19, the said shanks being pivotally joined for movement toward each other, and the said magnetic material forming part of each of the said shanks for attracting the same toward each other.

25. An engaging contact element for an electrical connecting means including an engaging cont-act element and a receiving contact element, the said engaging contact element comprising an electrically conductive component and a magnetic component, the said conductive component forming at least part of the outside of said engaging element for the purpose of making electric contact with a coacting receiving contact element.

26. An engaging contact element according to claim 25, wherein the said electrically conductive component is in form of a generally tubular member and wherein the said magnetic component is disposed within said tubular member.

27. An engaging contact element according to claim 26, wherein the said magnetic component is in form of a liner within said tubular member.

28. An engaging contact element according to claim 26, wherein the said magnetic component is in form of a solid core within said tubular member.

29. An electrical connecting means comprising an engaging contact element and a receiving contact element defining a space for inserting therein the engaging contact element, said engaging contact element having an electrically conductive component forming at least part of the outer wall surface of the said component and said receiving contact element having an electrically conductive component forming at least part of the wall surface defining said space, the said conductive wall surfaces of the two elements being in loose contact engagement, one with the other, upon insertion of the engaging contact element in the receiving contact element, and magnetic means including two portions supported by said contact elements in a spatial and magnetic relationship in which the mutual magnetic attraction between said two portions acts upon said conductive components in a direction such as to press said engaging conductive wall surfaces toward each other thereby magnetically increasing the contact pressure therebetween.

References Cited in the file of this patent UNITED STATES PATENTS 

